1. Field of the Invention
This invention relates to mixers in general and more particularly to a sub-harmonic mixer that has improved electrical performance in a small package size.
2. Description of Related Art
A mixer circuit converts a radio frequency (RF) signal to an intermediate frequency (IF) signal which is the difference of the RF and a local oscillator (LO) signal. The IF frequency is obtained by multiplying the RF signal with the local oscillator (LO) signal. The difference or IF frequency is a result of the non-linearity of the mixer. Along with the IF frequency, the mixer typically generates inter-modulation products due to the non-linearity response.
The isolation between the local oscillator port and the radio frequency port is called L-R isolation. In a mixer, there is parasitic coupling that results in some of the LO signal leaking into the RF port. If the LO signal frequency is close to the RF signal frequency, the parasitic coupling is difficult to filter at the RF port.
While various mixers have been used, a continuing need exists for a mixer that has improved electrical performance in particular improved L-R isolation, that is compact and that can be manufactured at low cost.